The shutdown of the Mt. Tom power plant in Holyoke earlier this month signals the end of decades of using coal for generating electricity in Massachusetts.

Mt. Tom, which stopped operating
as of June 2, will officially close by October, the last of the state’s three coal plants to schedule a permanent shutdown. Salem Harbor Power Station in Salem closed, as previously planned, onJune 1, while Brayton Point in Somerset is scheduled to stop operating in 2017.

The transition from coal will help lower greenhouse gas emissions, but it also brings challenges. Among the questions: how to replace the plants’ generating capacity to meet future demand, and how to support their host communities, which have long relied on the facilities as big taxpayers and employers.

“Good, bad, or indifferent, whatever people feel about those facilities, they have been employers,” said Alicia Barton, chief executive of the Massachusetts Clean Energy Center, a quasi-public agency charged with helping these communities as the state moves to cleaner fuels.

The demise of coal in Massachusetts — a goal long sought by environmental and health advocates — comes as cheap, domestic natural gas and tougher pollution regulations have combined to make coal-fired generation too expensive. Less than two decades ago, more than one-quarter of the electricity produced in Massachusetts was generated with coal, according to the US Energy Department.

GDF Suez Energy Generation North America, the owner of Mt. Tom, had long considered closing the plant, which employs 28. John Shue, vice president of operations in New England, said the company recently determined that the cost of upkeep combined with the improvements needed to meet new emissions standards was just too much.

“In my personal opinion,” Shue said, “coal for the near term in Massachusetts is pretty much over.”

‘In my personal opinion, coal for the near term in Massachusetts is pretty much over.’

Coal’s decline has accelerated in recent years, particularly as the controversial drilling technique known as fracking has opened new natural gas reserves and lowered the cost of the cleaner-burning fossil fuel.

Growing concerns about climate change have added to the pressure. All fossil fuels produce greenhouse gases such as carbon dioxide, but burning coal emits the largest amount. Coincidentally, on the day that GDF Suez announced Mt. Tom’s retirement, the US Environmental Protection Agency issued a proposed rule that would require existing power plants to cut carbon emissions by 30 percent from 2005 levels within 15 years.

Research from Georgetown Climate Center shows that since 2005, Massachusetts already has reduced its carbon emissions by 47 percent, partly because of the decline in coal use.

Barry Chin/Globe Staff/File 1997

In this 1997 photo, activists from groups including the American Lung Association and the Appalachian Mountain Club gathered outside the Salem power plant, seeking its closure.

Today, natural gas generates nearly two-thirds of the state’s electricity, but the growing reliance on gas has become a concern to New England energy officials. Pipelines that transport the gas don’t always have enough capacity to handle the demand for the fuel, leading to temporary shortages and spikes in wholesale prices.

Energy officials worry that the problem will get worse as demand for natural gas grows. Salem Harbor’s owner, for example, plans to replace the coal plant with a natural gas-fired facility.

New or expanded pipelines could ease the problem, but they are controversial in the communities they would cross. Environmentalists also question whether substituting one fossil fuel for another is the best way to attack climate change, which is becoming a greater threat.

David L. Ryan/Globe Staff

The Salem Harbor power station was shut down on June 1.

the “Filthy Five,” the region’s dirtiest power plants. Salem Harbor, Mt. Tom, and Brayton Point were all on the list.

So were two oil-burning plants, Canal Generating Station in Sandwich, now owned by NRG, and Mystic Generating Station, on the border of Everett and Charlestown, now owned by Exelon Power. Both of those facilities are now are capable of burning natural gas.

“For the state, for the administration, it’s an opportunity because obviously the [plant] retirements are good for meeting our targets for global warming pollution,” said Claire B.W. Miller, state director for the Toxics Action Center, a regional group advocating for clean air and water.

Brian Kenney, business manager for the International Brotherhood of Electrical Workers Local 455, which represents most of Mt. Tom’s employees, said anyone advocating for the end of coal is being shortsighted.

Matthew Cavanaugh/Boston Globe

The Mt. Tom coal-fired power plant in Holyoke was shut down on June 2.

“I have got to believe that there is a place in the industry for coal,” Kenney said. “By allowing these plants to close, I think they’re really jeopardizing keeping the lights on.”

He said his biggest concern is making sure Mt. Tom’s workers find new jobs with the company or are adequately compensated for their years of service.

“These are very senior guys,” he said. “ Their working career for the most part has been at the Mt. Tom power plant.”